1. Field of the Invention
This invention relates to ultrasonic scanning and more particularly to ultrasonic scanning of radii in composite structures.
2. Description of the Related Art
Composite structure designed for aerospace applications often contains radiused xe2x80x9cIxe2x80x9d, xe2x80x9cUxe2x80x9d or xe2x80x9cTxe2x80x9d intersections. For design reasons, these intersections have some sort of external radius (ie., they do not have sharp corners), and contain an internal filer material of some sort, called a xe2x80x9cnoodle.xe2x80x9d The quality of the noodle, its interface with the composite plies, and the consolidation of the plies, are all critical to proper joint functioning. The quality of the intersection of webs and flanges in composite spars, or webs and skins in co-cured structure are critical to their performance. Flaws, such as cracks, voids, or delaminations can form in this region, and adversely affect the structure. However, these radiused regions are not easy to inspect well.
Up to this point, the inspection of radiused noodle regions of composite spars and co-cured structures has been a time-consuming, labor-intensive procedure that has shown questionable consistency. Timely, accurate, and reliable non-destructive characterization of these regions is very important, and is the problem this invention adresses.
Until now, inspection of radiused regions has done by hand using a UT transducer in pulse-echo mode with a radiused shoe mounted on its end. The operator holds the shoe against the inner radius of the part, sliding it along the length, and rocking it back and forth over a near 90xc2x0 angle. He/she is looking for flaw indications that will reflect the ultrasound back to the transducer, to be picked up and indicated by changes in a amplitude/time trace on an oscilloscope. He must determine xe2x80x9con the flyxe2x80x9d whether or not the UT reflection amplitude is high enough and (at the same time) the extent of the flaw is also great enough to disqualify the part. The inspector will utilize a radius flaw standard a pre-determined NDI criteria for flaw amplitude and length.
There are significant problems with this approach. First, it is costly and time consuming to inspect the radii by hand. It is slow work, and ties up an inspector the entire time. The rest of the structure is inspected in an automated fashion on a UT scanning system. Second, this method is operator dependent, and subject to potential errors. The operator must watch an oscilloscope, looking for signal changes, while moving the transducer in the radial and axial directions by hand. The flaw indications are often subtle, must be tracked at multiple angles, and complete coverage of the radii is sometimes difficult to ensure. Third, the existing method does not provide reviewable image data. No data is saved to be analyzed later, nor can it be reviewed if there are any questions. Fourth, the current method does not produce images that show the size or length of any indications that are found. The inspector simply marks the measured length of an indication on the part itself.
There are multiple transducer automated UT scanning systems that make use of multiple transducers in a variety of orientations. However, with the present invention, only a single transducer is needed at the radii, and costly multiple channel pulser/receiver systems are not required.
Patent Literature
U.S. Pat. No. 4,980,872 shows an ultrasonic probe coupled to an extension arm which can be mounted to a movable carriage. The angle of the probe can be manually controlled from the opposite end of the extension arm via a mechanical linkage. U.S. Pat. No. 4,807,476 describes an ultrasonic inspection system for inside radii comprised of a shoe having a single transducer. The signal is directed by two reflectors, one fixed which turns the signal 90 degrees and another that can be rotated and reflects the signal at 90 degrees again, but by rotation can cover all angles required to inspect the entire radius. The control system causes the probe to traverse the area in multiple passes while changing the angle at each pass to create a raster scan image. J U.S. Pat. No. 4,612,808 discloses a gimballed ultrasonic probe head with special gimbal geometry so that when used to inspect the junction 9 of a pipe with a cylinder, it will always keep the probe pointed toward the axis of the pipe. U.S. Pat. No. 4, 526,037 describes a mechanism for keeping two ultrasonic probes, one on either side of an outside corner, aligned as they are rotated around the saddle contour formed by the junction of an inlet nozzle and a reactor vessel. As part of the mechanism, the probes are pivotably mounted to either end of a rocker arm. U.S. Pat. No. 4,117,733 also describes a system for ultrasonic inspection of the junction of a nozzle with a pressure vessel. Ultrasonic transducers are pivotably mounted on arms which also pivot with respect to a central shaft to allow inspection at various radial distances from the central shaft.
Systems of the prior art for ultrasonic inspection of radii utilizing a number of transducers fixed at various angles and mounted to a carriage or machine can be contrasted to the present system where only a single transducer is needed at the radii.
The present invention utilizes an opposed pair of water coupled ultrasonic transducer mounted in fingers with a suitable and radius to fit the fillet radius. The base of each finger is mounted to a hand and is free to rotate about an axis parallel to the longitudinal axis of the part to be inspected. The hands are mounted to arms via a three-position connection so they can be rapidly reconfigured for inspecting upper and lower radii and the webs of the parts. The arms are mounted at their upper ends by two vertically spaced bearings riding on shafts that project horizontally from a base structure. The arms are pulled toward one another by a rubber band stretched between them. The base structure couples the mechanism to a gantry robot. In operation the mechanism is moved into position so the fingers ride in the desired radii at a desired angle, and a longitudinal sweep is made to collect data. The vertical position of the sensor system is then changed slightly, which changes the angle of the fingers, and another longitudinal sweep is made. This is repeated until all desired angles are covered.